First we need to know your pc's spec's , operating system , video drivers , background programs that are running (such as fire walls/AV's ect )
Such as 
2.0 ghz Amd 
512 ram
gf 4 mx 400   30.85 drivers  Direct X 8.1
win 98 se 
microtrends AV program  , set to manual scan 
700kbps Dsl connection